Water hardness, caused by dissolved minerals, can be removed through various chemical reactions. The specific approach depends on the type of hardness: temporary or permanent.
Understanding Water Hardness
- Temporary Hardness: This type is caused by dissolved bicarbonates of calcium and magnesium. It can be removed by boiling or by adding lime (calcium hydroxide).
- Permanent Hardness: This is caused by dissolved sulfates and chlorides of calcium and magnesium. It requires more complex methods such as adding washing soda or using an ion exchange resin.
Removing Temporary Hardness Through Chemical Reactions
The key reactions involved in removing temporary hardness by boiling are:
| Reactant | Reaction | Products |
|---|---|---|
| Calcium Bicarbonate | Ca(HCO3)2(aq) → CO2(g) + H2O(l) + CaCO3(s) | Carbon Dioxide, Water, Calcium Carbonate |
| Magnesium Bicarbonate | Mg(HCO3)2(aq) → CO2(g) + H2O(l) + MgCO3(s) | Carbon Dioxide, Water, Magnesium Carbonate |
Explanation of the reactions
- Heating: When water containing calcium bicarbonate or magnesium bicarbonate is heated, the heat triggers a chemical reaction.
- Decomposition: The bicarbonate compounds decompose into carbon dioxide gas, water, and an insoluble carbonate precipitate.
- Precipitation: The insoluble calcium carbonate (CaCO3) or magnesium carbonate (MgCO3) forms a solid precipitate. This precipitate settles out or can be removed by filtration, softening the water.
The reference states: The reaction(s) involved in the removal of temporary hardness of water by heating is/are: Ca(HCO3)2(aq)→CO2(g)+H2O(l)+CaCO3(s) Mg(HCO3)2(aq)→CO2(g)+H2O(l)+MgCO3(s)09-Jan-2020
Practical Applications
- Boiling: Boiling is a simple method to remove temporary hardness for household use.
- Lime Softening: In industrial settings, adding lime (calcium hydroxide) promotes the same type of reactions, causing the precipitation of calcium and magnesium carbonates.
Removing Permanent Hardness Through Chemical Reactions
Permanent hardness requires different chemical treatments:
- Washing Soda (Sodium Carbonate): Adding washing soda causes a precipitation of calcium and magnesium carbonates from their sulfates or chlorides.
- Ion Exchange: This method involves using resins to swap out calcium and magnesium ions with less problematic ions like sodium. This does not cause a precipitate, but it does effectively remove the hardness ions.
Summary
- Temporary hardness is removed by boiling or adding lime, which leads to the formation of insoluble carbonates.
- Permanent hardness requires the use of washing soda or ion exchange to remove the calcium and magnesium ions.
